The monster object is located about 250 million light years away, in a galaxy named NGC 1277 - which is less than a tenth the size of our own Milky Way.

"This is a really oddball galaxy," said study team member Karl Gebhardt of the University of Texas at Austin in a statement. "It's almost all black hole. This could be the first object in a new class of galaxy-black hole systems."

Above: the galaxy NGC 1277

Researchers said they had to take a year to double check their calculations because the massive size of the black hole seemed so unusual.

They added that the hole is 11 times as wide as the orbit of Neptune.

Black holes are usually formed when massive stars collapse into themselves at the end of their lives. But the sheer size of NGC 1277 indicates other forces are at work as well.

The black hole was found by surveying 700 galaxies with the Hobby-Eberly Telescope at the University of Texas at Austin's Mcdonald Observatory.

They found six galaxies with objects moving very fast inside them - about 218 miles per second - and theorised that meant unusually large black holes would be found at their centre.

The lead author of the study, Remco van den Bosch, told Space.com that the black hole may be a relic of the big bang, when the universe was formed.

"It could just be this thing has been sitting around since the Big Bang eand not done much since then," he said. "It might be a relic of what star formation and galactic formation looked like at that time."